Jean-Charles Buffet

Synthesis, Characterization, and Lactide Polymerization Activity of Group 4 Metal Complexes Containing Two Bis(phenolate) Ligands

A series of group 4 metal complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2), Zr-(5)(2), Hf-(1)(2), and Hf-(4)(2) containing two bridged bis(phenolate) ligands of the (OSSO)-type were prepared by the reaction of the corresponding bis(phenol) and group 4 metal precursor MX(4) (X = O(i)Pr, CH(2)Ph) and isolated as robust, colorless crystals. NMR spectra indicate D(2) symmetry, in agreement with the solid state structure determined by single crystal X-ray diffraction study of the complexes Zr-(1)(2), Hf-(1)(2), Zr-(3)(2), Zr-(4)(2), and Zr-(5)(2). The complexes with the 1,4-dithiabutanediyl bridged ligands exhibit a highly symmetric coordination around the metal center. The introduction of the rigid trans-1,2-cyclohexanediyl bridged ligands led to a distorted coordination around the metal center in Zr-(4)(2) and Zr-(5)(2) when the ortho substituent is tert-butyl and the para substituent is larger than methyl. The complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2) as well as Hf-(1)(2) and Hf-(4)(2) initiated the ring-opening polymerization of meso-lactide at 100 °C to give heterotactic polylactide with pronounced heterotacticity (>70%) and varying polydispersity (1.05 < M(w)/M(n) < 1.61). As shown by kinetic studies, zirconium complex Zr-(1)(2) polymerized meso-lactide faster than the homologous hafnium complex Hf-(1)(2).

Synthesis and characterisation of aqueous miscible organic-layered double hydroxides

We report the synthesis and characterisation of a new family of layered double hydroxides entitled Aqueous Miscible Organic Layered Double Hydroxide (AMO-LDH). AMO-LDHs have the chemical composition [Mz+1−xM′y+x(OH)2]a+(Xn−)a/r·bH2O·c(AMO-solvent) wherein M and M′ are metal cations, z = 1 or 2; y = 3 or 4, 0 < x < 1, b = 0–10, c = 0–10, X is an anion, r is 1–3 and a = z(1 − x) + xy − 2. The role of the AMO-solvents such as acetone (A) or methanol (M) in the LDH synthesis is discussed. The distinguishing features between AMO, and conventional or commercial LDHs are investigated using X-ray diffraction, infrared spectroscopy, electron microscopy, thermal analysis, adsorption and powder density studies. These experiments show that AMO-LDHs are highly dispersed and exhibit significantly higher surface areas and lower powder densities than conventional or commercially available LDHs. AMO-LDHs can exhibit N2 BET surface areas in excess of 301 m2 g−1 compared to 13 m2 g−1 for the equivalent LDHs prepared by co-precipitation in water. The Zn2Al–borate LDH exhibits a pore volume of 2.15 cm3 g−1 which is 2534 times higher than the equivalent conventionally prepared LDH.

Ethylene polymerisation using solid catalysts based on layered double hydroxides

We report here the use of methylaluminoxane (MAO) modified aqueous miscible organic solvent treated (AMOST) layered double hydroxide, Mg6Al2(OH)16CO3·4H2O (AMO-Mg3Al-CO3) as a catalyst support system for the slurry phase polymerisation of ethylene using immobilised metallocene and non-metallocene metal complexes. The polymerisation data demonstrates that the catalyst productivity is dependent on the thermal treatment of the LDH and the temperature, pressure and time of the polymerisation. The solid catalyst system, AMO-Mg3Al-CO3/MAO/(MesPDI)FeCl2 has been shown to have the highest overall activity for a non-metallocene system (14166 kgPE mol−1complex h−1 bar−1), and AMO-Mg3Al-CO3/MAO/(2-Me,4-PhSBI)ZrCl2 was the most productive for a metallocene-based system (∼3300 kgPE mol−1complex h−1 bar−1). The molecular weights and polydispersities vary with the complex on the AMO-LDH surface. Scanning electron microscopy images show that the morphology of the as produced polyethylene mimics that of the LDH support.

Synthesis and characterisation of permethylindenyl zirconium complexes and their use in ethylene polymerisation

We report the synthesis of two zirconocenes, dimethylsilylbis(hexamethylindenyl) zirconium dichloride, rac-(SBI*)ZrCl2, and nbutyldimethylsilyl(hexamethylindenyl) zirconium trichloride, [(Ind*SiMe2nBu)Zr(μ-Cl)Cl2]2. The complexes were characterised by NMR spectroscopy and X-ray crystallography, and the bonding was evaluated using density functional theory. rac-(SBI*)ZrCl2 demonstrated a very high activity for solution phase polymerisation of ethylene (ca. 22 500 kgPE−1 molZr−1 h−1 bar−1). Both rac-(SBI*)ZrCl2 and rac-(EBI*)ZrCl2 (EBI* = ethylenebis(hexamethylindenyl)) have been supported on MAO modified silica and AMOST layered double hydroxides (AMO-LDHs), and evaluated as catalysts in the slurry-phase polymerisation of ethylene. The highest catalytic polymerisation activities for rac-(SBI*)ZrCl2 and rac-(EBI*)ZrCl2 on the layered double hydroxides were 9657 and 4325 kgPE−1 molZr−1 h−1 bar−1 respectively, for MAO modified Mg2Al–SO4 LDH. However, rac-(EBI*)ZrCl2 was a three times more active catalyst than rac-(SBI*)ZrCl2 when supported on silica.

Hydrodeoxygenation of water-insoluble bio-oil to alkanes using a highly dispersed Pd–Mo catalyst

Bio-oil, produced by the destructive distillation of cheap and renewable lignocellulosic biomass, contains high energy density oligomers in the water-insoluble fraction that can be utilized for diesel and valuable fine chemicals productions. Here, we show an efficient hydrodeoxygenation catalyst that combines highly dispersed palladium and ultrafine molybdenum phosphate nanoparticles on silica. Using phenol as a model substrate this catalyst is 100% effective and 97.5% selective for hydrodeoxygenation to cyclohexane under mild conditions in a batch reaction; this catalyst also demonstrates regeneration ability in long-term continuous flow tests. Detailed investigations into the nature of the catalyst show that it combines hydrogenation activity of Pd and high density of both Brønsted and Lewis acid sites; we believe these are key features for efficient catalytic hydrodeoxygenation behavior. Using a wood and bark-derived feedstock, this catalyst performs hydrodeoxygenation of lignin, cellulose, and hemicellulose-derived oligomers into liquid alkanes with high efficiency and yield.Bio-oil is a potential major source of renewable fuels and chemicals. Here, the authors report a palladium-molybdenum mixed catalyst for the selective hydrodeoxygenation of water-insoluble bio-oil to mixtures of alkanes with high carbon yield.

Selective ethylene oligomerisation using supported tungsten mono-imido catalysts

A series of substituted phenyl mono-imido complexes of the type W(NR)Cl4(THF) (R = C6H5, 2,6-Me-C6H3, 3,5-Me-C6H3, 2,4,6-Me-C6H2, 4-OMe-C6H4, 2,6-F-C6H3 and 3,5-CF3-C6H3) have been synthesised and characterised. Reaction of these complexes with solid polymethylaluminoxane (sMAO) leads to immobilisation and in situ methylation of the chloride positions on the surface of the support. Reaction of W(NR)Cl4(THF) with trimethylaluminium (TMA) yields the trimethyl complexes W(NR)Me3Cl. Immobilisation of the isotopically labelled W{N(2,6-F-C6H3)}(13CH3)3Cl on sMAO furnished the supported complex with two identifiable methyl resonances in the 13C–{1H} solid state CPMAS spectrum (45 and 56 ppm), with the latter matching the unsupported complex, confirming retention of the structure on the surface. The sMAO-supported complexes (W : Al = 1 : 150) were tested for their propensity to dimerise ethylene (1 bar) in d6-benzene at 100 °C and compared with the previously reported sMAO-W{N(2,6-iPr-C6H3)}Cl4(THF) (sMAO-1.a). Complexes with electron deficient imido groups were shown to be the most active, and increased steric bulk in the ortho positions is also an important factor, with sMAO acting as a support, scavenger and activator. sMAO-W{N(3,5-CF3-C6H3)}Cl4(THF) was the most active, demonstrating a turnover frequency of 5.65 molC2H4 mol−1W h−1 and a selectivity towards 1-butene of 91% after 8 h.

Controlling the Surface Hydroxyl Concentration by Thermal Treatment of Layered Double Hydroxides

Layered double hydroxides (LDHs) are important materials in the field of catalyst supports, and their surface hydroxyl functionality makes them interesting candidates for supporting well-defined single-site catalysts. Here, we report that the surface hydroxyl concentration can be controlled by thermal treatment of these materials under vacuum, leading to hydroxyl numbers (αOH) similar to those of dehydroxylated silica, alumina, and magnesium hydroxide. Thermal treatment of [Mg0.74Al0.26(OH)2](SO4)0.1(CO3)0.03·0.62(H2O)·0.04(acetone) prepared by the aqueous miscible organic solvent treatment method (Mg2.84Al-SO4-A AMO-LDH) is shown to yield a mixed metal oxide above 300 °C by a combination of thermogravimetric analysis, powder X-ray diffraction (PXRD), BET surface area analysis, and FTIR spectroscopy. PXRD shows the disappearance of the characteristic LDH 00l peaks at 300 °C indicative of decomposition to the layered structure, coupled with a large increase in the BET surface area (95 vs 158 m2 g-1 from treatment at 275 and 300 °C, respectively). Titration of the surface hydroxyls with Mg(CH2Ph)2(THF)2 indicates that the hydroxyl number is independent of surface area for a given treatment temperature. Treatment at 450 °C under vacuum produces a mixed metal oxide material with a surface hydroxyl concentration (αOH) of 2.14 OH nm-2 similar to the hydroxyl number (αOH) of 1.80 OH nm-2 for a sample of SiO2 dehydroxylated at 500 °C. These materials appear to be suitable candidates for use as single-site organometallic catalyst supports.

Water adsorbancy of high surface area layered double hydroxides (AMO-LDHs)

Understanding the water adsorbancy of highly dispersed, high surface area layered double hydroxide (LDH) is of great importance as it directly relates to their hydrophobicity and subsequent use as additives in LDH-polymer nanocomposites. In this study, we have investigated the water vapour uptake response of highly dispersed, high surface area aqueous miscible organic-LDHs (AMO-LDHs) in two relative humidity atmospheres (RH99 and RH60) at 20 °C. We observed that AMO-Mg3Al–CO3 and AMO-Zn2MgAl–CO3 exhibited very high water vapour uptake in an RH99 atmosphere at 20 °C (56 wt% and 20 wt% for Mg3Al–CO3 and Zn2MgAl–CO3 LDH respectively after 120 h). The crystallinity in both ab-plane and c-axis of the LDHs increased with increasing exposure uptake. The water vapour adsorption capacity of the AMO-LDHs can be dramatically reduced by treatment with stearic acid.